"Michael S. Tsirkin" <mst@xxxxxxxxxx> writes: > On Mon, Jun 03, 2013 at 09:56:15AM +0930, Rusty Russell wrote: >> "Michael S. Tsirkin" <mst@xxxxxxxxxx> writes: >> > On Thu, May 30, 2013 at 08:53:45AM -0500, Anthony Liguori wrote: >> >> Rusty Russell <rusty@xxxxxxxxxxxxxxx> writes: >> >> >> >> > Anthony Liguori <aliguori@xxxxxxxxxx> writes: >> >> >> Forcing a guest driver change is a really big >> >> >> deal and I see no reason to do that unless there's a compelling reason >> >> >> to. >> >> >> >> >> >> So we're stuck with the 1.0 config layout for a very long time. >> >> > >> >> > We definitely must not force a guest change. The explicit aim of the >> >> > standard is that "legacy" and 1.0 be backward compatible. One >> >> > deliverable is a document detailing how this is done (effectively a >> >> > summary of changes between what we have and 1.0). >> >> >> >> If 2.0 is fully backwards compatible, great. It seems like such a >> >> difference that that would be impossible but I need to investigate >> >> further. >> >> >> >> Regards, >> >> >> >> Anthony Liguori >> > >> > If you look at my patches you'll see how it works. >> > Basically old guests use BAR0 new ones don't, so >> > it's easy: BAR0 access means legacy guest. >> > Only started testing but things seem to work >> > fine with old guests so far. >> > >> > I think we need a spec, not just driver code. >> > >> > Rusty what's the plan? Want me to write it? >> >> We need both, of course, but the spec work will happen in the OASIS WG. >> A draft is good, but let's not commit anything to upstream QEMU until we >> get the spec finalized. And that is proposed to be late this year. > > Well that would be quite sad really. > > This means we can't make virtio a spec compliant pci express device, > and we can't add any more feature bits, so no > flexible buffer optimizations for virtio net. > > There are probably more projects that will be blocked. > > So how about we keep extending legacy layout for a bit longer: > - add a way to access device with MMIO > - use feature bit 31 to signal 64 bit features > (and shift device config accordingly) By my count, net still has 7 feature bits left, so I don't think the feature bits are likely to be a limitation in the next 6 months? MMIO is a bigger problem. Linux guests are happy with it: does it break the Windows drivers? Thanks, Rusty. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
